This invention relates to a novel organoboron complex initiator system and an acrylic adhesive composition containing this initiator. More particularly this invention involves a two-part initiator system comprising in one part a stable organoboron amine complex and in the second part an aldehyde destabilizer or activator. This initiator system is especially useful in elastomeric acrylic adhesive compositions and provides a room temperature, relatively slow curing system with good adhesive properties.
Adhesive compositions including acrylic adhesives such as solutions of elastomeric polymers in soluble polymerizable acrylic or methacrylic monomers are well known in the art. These compositions which are especially known for their toughening properties generally include a redox system which comprises a catalyst or initiator, an accelerator and an activator to initiate cure, as well as other additives such as adhesion promotors, chelators, cross-linking agents, thickeners and plasticizers. Two-part acrylic adhesives where an activator is added as a separate second component are widely used and are known for curing speed as well as toughness. The catalyst or initiator typically used in these adhesives are free-radical initiators of the organic peroxy or hydroperoxy type, perester or peracid type.
Many known adhesive systems, such as the epoxies, require a thermal cure to obtain desirable properties, while other that do not, usually require prolonged cure times.
Boron amine complexes have been utilized in catalyst systems to polymerize olefin compounds as disclosed in U.S. Pat. No. 3,275,611 issued on Sep. 27, 1966 to E. H. Mottus, et al. The use of boron amine complexes as a dental adhesive has been disclosed in a publication to S. Fujisawa, et al., Chem. Abstracts 88532r, Vol. 73 (1970) where an amine acceptor such as an isocyanate acid chloride, or sulfonyl chloride is added to reactivate the initiator. Further use of boron amine complexes in adhesive compositions has been disclosed in copending application Ser. No. 07/692,766 filed Apr. 29, 1991 now U.S. Pat. No. 5,106,928, where an organic acid destabilizer or activator is added to the composition. These systems provide relatively fast curing compositions while the organoboron aminealdehyde initiator containing compositions of this invention cure at room temperature at a somewhat slower curing rate making them particularly useful in applications where longer open times are required.